Tandem axle vehicle



June 4,1946. I E. w. LE ZKUS 2,401,687

TANDEM AXLE VEHICLE Filed June 27, 1944 2 Sheets-Sheet 1 INVENTOR. WOOD M4 L7z/r0$ 2 Sheets-Sheet 2 INVENTOR.

EL W000 wzErz/ras By 045% flffOR/V'? June 4, 1946. E. w. LETZKUS TANDEM AXLE VEHICLE Filed vJune 27, 1944 Patented June 4, 1946 UNITED STATES OFFICE a a 2,401,687 n e t a TANDEM AXLE vsarcta; Elwood W. Letzkns, sa es, the M y. Application June 27, 1944, seriarnat 'edoa v l r 3 C '7 Claims.

to multi-Wheelgvehicles; the type havinga pair This invention relates and particularly to those of of tandem axles atthe rear.

The primary object of the present inventionis to devise an arrangement of closely spaced tandem axles in which thewheels supporting said axles'will track properly with respect to the front dirigible wheels, so as to avoid drag and sending of the tires aswell a excessive wear and tear on the elements of the suspension.

My invention is chiefly concerned with obtain ing accurate tracking of the rear axleof a tandern pair, and although this object is not broadly nwpit has never been success-fully attained, due to lack of proper load distribution upon that axle insucli manner that the axle can shift ax ially, sideways of the vehicle, with relative freedomand without the introduction of damaging stresses and strains. 'Inthis connection, it is an object to utilize a multiple beam or compensat ing form of suspensionin which the rear-most axle of r the tandem pair is connected to the springs (beams) at points inside the longitudinal frame members of the chassis.

Preferably, the rearmost axle of the tandem pair is universally connected to the forward axle or tothe chassis at a point adjacent the forward axle, and I have found that the best tracking action is obtained when the universal connection is -made just'behind the center of the forward axla- This arrangement, then, becomes another veryimportant object of my invention.

The foregoing and other objects of. the present invention should. clearly appear from a study of the following detaileddescription when takenin conjunction with the; accompanying drawings.

In the drawings:

Fig, 1 represents a plan view of a portion of a vehicle chassis embodying my invention. As illustrated his the rear end of a truck or trailer, with both axles idle, but it might comprise a driven and an idle axle, and in any case the pair of axles might be disposed anywhere, longitudinally v of the frame.

Fig. 2 is a cross-sectional view taken substane tially along the plane of the line 2-2 in Fig. 1.

Fig. 3 is a vertical section taken-approximately upon the plane of line 3-3, Fig. 1, th springs being omitted.

Fig. 4 represents a vertical section taken upon the plane of line 44, Fig. 3.

Fig. 5 is another vertical section, on the plane of line 5-5, Fig. 4, with the axle omitted.

With continued reference to the drawings, a conventional chassis frame 8 is disposed above a pair oftandemaxles '9 and Ill, supported by a plurality of' wheels l2. A load equalizing form of suspension comprising two pairs of beams l3, it (preferably spring leafassemblies) is interposed between the axles and the frame and connected thereto as follows. i l I The beams l 3: are pivoted at their forward ends on theoutsideof the frame at l5, secured. intermediate their endsto the axle 9 by brackets l6, and connected attheir rear ends by shackles I"! to apair of bars l3 that are welded or otherwise secured to a cross-trunnion 59. The latter i journaled in apair of blocks 20 that are.se cured: to wtheframe at points substantially. midway betwe'enthe axles. A second set of bars, 22, are secured to the trunnion at points inside the frame channels andfconnected by shackles-23 to the-front e'nds of theuspringsaM, the rear ends of=whichp are pivotedron the frame at 24. Except for disposition of-the springs l4 inside the longitudinal channels, all of the above is substantially conventional. a l 1 ,1 1 The:springi.-bearnsi ld'are connectedto the rear axler.=ill'by meansrcomprising'z an arcuate track 26,:of inverted iJ-shapefsecured in any suitable mannerrto the springs; an arcuate rail 28 complementalnto the track and secured toseveral lugs 2i, 21 whichin turn are welded to the axle; .aplurality .of bearing rolls 29, disposed in grooves, between the rail and the top wall of the track; and several guiderollers 30 carried in slots liltinsthe rail and having integral pins 32 journaled. in the side walls of the track. Preferably,, there are,three slots and three groups of rollers, to distribute the load upon the ends and the centerportion of the axle.

Theload.is appliedrdownwardly from springs to axle chiefly through the rollers 29, which act directly against the rail 28, the latter in turn transmitting the thrust directly to the axle lugs 27, 2'5". The rollers may transmit part of the load, and their pins 32 serve to prevent separation of springs and axle as well as to cooperate'in limiting lateral'movement in either direction of the rail with respect to the track. Normally,

when the vehicle is traveling a straight path, the

' rollers 39 are midway between the ends of their respective slots 33, and they engage the end of the slots to limit lateral swinging (tracking) of the axle only when the vehicle is rounding a relatively sharp curve at relatively high speed.

The arcuate rail and its complemental'track have such radius as to permit the rear axle to swing about a point (3'!) just behind the center of the forward axle. This relationship is: maintained by a central radius rod -85 and two wishbone radius rods 36, welded at their rear ends to the rear ends to the rear axle and its attached lugs 21, 21, and joined at their front ends in an apex that is universally connected to the frame by a ball-headed pin 31. The pin -31 is screwed into a depending cross-member 38 of the framework.

It should be understood that the radius rods might be connected to a central rearward bracket on the axle instead of to the frame (or to the differential housing in case the forward axle is driven); and that in the case of a dual drive, a

torque tube between the two differential housings can take the place of the radius rod 35.

Further, the rods 35, 36 also serve as torque rods when brakes are applied to the wheels of a rear trailing axle. In this connection, disposition' of the spring beams inside the side frame 3 members serves to permit the addition of ,brak- 1.

ing equipment ,at thewaxle ends ,without Timerfering with free lateralgswinging of the rear axle relative to its track 26. U The operation should now be fairly clear.

Both axles are permitted to rise and fall and tilt freely, no interference being offered by the mechanism added to facilitate tracking of the wheels. In response to road curvatures and unevenness and shifting load the rear axle is permitted to swing laterally about the vertical axis of the pin 31, the rail 28 shifting with the axle l0 while the track 26 is held always in its illustrated po sition by the beams Hi. This sliding lateral movement is facilitated by the rollers 29 and 30, which also serve to distribute the load properly upon the axle.

Obviously, changes may be made within the scope of the invention, and therefore I wish to be limited, as is customary, only by reasonably liberal interpretation of the appended claims.

What is claimed is: p

1. In a vehicle comprising a chassis frame having tandem wheel-supported axles disposed therebeneath, the frame embodying longitudinal side members adjacent the axle ends, a longitudinally arranged suspension for mounting said frame relative to said axles, guide means upon the rearmost axle to permit it to shift transversei of the vehicle, said suspension connected to said guide means at points located inside said longitudinal frame members. v

2. In the vehicle defined in claim 1, said susension being supported by the forward axle at points" outside of said longitudinal frame members.

3. In a vehicle embodying a frame and a rear axle disposed below one end thereof, a suspension connected to said frame, and means for connecting said suspension to said rear axle, said means comprising an arcuate channel in the form of a guide track and a complemental arcuate rail.

nested therein, directly above said rear axle and extending substantially from end to end thereof,

both horizontally disposed with one attached to said suspension and the other attached to the axle, and anti-friction means associated with said track and rail to facilitate relative slidin closely spaced axles beneath said frame, suspension mechanism connected to said frame and to the forward axle, an arcuate track in the form of an inverted channel connected to said mechanism and disposed adjacent to and extendingfrom end to end of the rear axle of the pair, an

'arcuate rail slidably disposed within said channel and secured to the rear axle, a plurality of rollers disposed between said rail and the top of said channel, and means preventing vertical separation of said bar and said channel while permitting the former to oscillate endwise within the latter. 7

6. In the combination defined in claim 5, said preventing means comprising a plurality of lateralslots through said rail, and a corresponding plurality of rollers disposed in said slots and having their ends projecting into the side walls of said channel.

7. In a vehicle having a framework with a pair of tandem axles disposed beneath a portion thereof and suspension mechanism for connecting said axles to said framework, means attaching the forward axle to said mechanism for substantiall vertical and tilting movements only, and guide means connecting the rearward axle to said mechanism with capacity for an additional endwise movement laterally of the frame, said guide means comprising an arcuate rail, secured to said rearward axle with its'center of radius locatedadjacent the center of the forward axle, said rail having radial grooves in its .top surface and rollers disposed in said grooves, an arcuate track member of inverted channel shape slidably receiving said rail and attached to the suspension mechanism, and means interconnecting said rail and said track member.

ELWOOD W. LETZKUS. 

